Holstein bull calves (n = 36) weaned at 6 wk of age were used in six trials to examine the response of N balance to postruminal administration of lysine with or without methionine in postweaned calves receiving diets based on corn and corn gluten meal. Calves were younger than 3 mo of age in Trials 1 and 2 but older than 3 mo in Trials 4 to 6. L-Lysine monohydrochloride was supplemented with or without DL-methionine twice daily through the reticular groove, except in Trial 4, in which N supplements were infused through duodenal cannulas. L-Glutamine was used as a nonspecific N source in every trial, and casein was a positive control in Trials 4 and 5. When daily CP intake from the diet was 3.9 g/kg BW, lysine was limiting for calves less than 11 wk of age (Trials 1 and 2) but not limiting for calves greater than 12 wk of age (Trial 3). No amino acid seemed to be limiting for calves greater than 20 wk of age (Trial 4) when daily CP intake was 4.1 g/kg BW, but lysine was limiting when CP intake was restricted to 3.0 g/kg BW when calves were more than 17 wk of age (Trial 5). However, lysine was not limiting above 18 wk of age (Trial 6) when CP intake was increased to 3.8 g/kg BW by adding urea to the diet. Results suggest that lysine may be limiting for corn and corn gluten meal diets only when ruminal microbial protein synthesis is restricted.